Where do I find instruction to decifer "TCCR2A = _BV(WGM21) | _BV(COM2A0);"?

Using Arduino Programming Questions
1

I was trying to follow a program written I think in C language. Came to a point where above
piece of code was written and could not determine what this code mean. I checked the C library
reference guide, but it didn't help me much.

// toggle pin 11 on compare
TCCR2A = _BV(WGM21) | _BV(COM2A0);
TCCR2B = _BV(CS20);

// 38kHz timer
OCR2A = (F_CPU/(IR_CLOCK_RATE*2L)-1);

Could anyone enlighten me, please.

2

This code is directly manipulating the microcontroller's registers (TCCR2A, TCCR2B, OCR2A). WGM21, COM2A0, CS20 are bit references within the registers. See the datasheet, http://www.atmel.com/Images/doc8271.pdf

_BV() is described in the AVR-Libc user's manual: AVR Libc Home Page

3

Those registers are for the timers. You will need to check the datasheet of the specific chip in question, but it's looking like a PWM output to me. Some will be setting what PWM mode to use, and I think the CS20 will be the prescaler bit to set. The OCR2A will be a compare register IIRC.